Commutator for an electrical machine

ABSTRACT

A commutator for an electrical machine, in particular for an electric motor for actuating drives in motor vehicles, has a commutator body that supports commutator laminations. To reduce the electromagnetic radiation, emitted into the environment as interfering radiation, that is engendered by spark development in the commutation operation, the commutator body is embodied as a hollow cylinder, and the commutator laminations are disposed on the inner jacket face of the commutator body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 2004/001119 filedon Jun. 2, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an improved commutator for an electricalmachine, in particular for an electric motor for actuating drives inmotor vehicles.

2. Description of the Prior Art

One commutator known from U.S. Pat. No. 6,285,106 B1 has ahollow-cylindrical commutator body of insulating material, which can bemounted on the rotor shaft of a commutator machine in a manner fixedagainst relative rotation, and on whose outer circumference thecommutator laminations are disposed with gap spacing from one another,side by side in the circumferential direction. Each commutatorlamination has an integral connection lug or connection hook forconnecting the coils of a rotor winding that is wound in a known mannerin slots of a ferromagnetic rotor body that is seated on the rotor shaftin a manner fixed against relative rotation. In order, to reduce thespark development which occurs in the commutation during operation ofthe commutator machine and which is the cause of electromagneticinterfering radiation, an indentation is machined into the face end ofthe commutator body facing away from the connection hooks, into whichindentation an interference suppressor disk, such as a varistor, isplaced such that one annular disk face of it rests on the bottom of theindentation, and the other annular disk face, carrying connectionelectrodes, points outward. A contact ring is pressed onto theinterference suppressor disk and electrically conductively connects theconnection electrodes with the commutator laminations. The contact ringhas a basic ring of insulating material, with many first and secondcontacts, each connected to one another. The number of first contactsand the number of second contacts is equivalent to the number ofcommutator laminations, or the equally large number of connectionelectrodes on the interference suppressor disk. Each first contact restson a connection electrode, and each second contact, electricallyconductively connected to the first contact, rests with mechanicalprestressing on the underside of one of the commutator laminations thatprotrude at the end past the indentation. A cap that presses the firstcontacts against the connection electrodes and that is locked in theindentation is pressed onto the contact ring.

SUMMARY AND ADVANTAGES OF THE INVENTION

The commutator of the invention has the advantage that because of theplacement of the commutator laminations on the inner jacket face of thecommutator body embodied as a hollow cylinder, which necessarily meansthe commutator brushes are located in the interior of the commutator,very good shielding against the electromagnetic interfering radiationengendered upon commutation is attained by the commutator itself, andadditional components for reducing spark development can be omitted.

In a preferred embodiment of the invention, the hollow-cylindricalcommutator body is of a material that shields against or absorbselectromagnetic radiation. As a result, additional damping of theelectromagnetic interfering radiation is also attained. For example, thecommutator body is of metal, and an insulation layer is disposed betweenthe commutator body and the commutator laminations. However, thecommutator body may also be made from plastic, and magnetically and/orelectrically conductive materials such as steel fibers or soot can beadmixed with the plastic or enclosed by a metal sleeve that shieldsagainst electromagnetic radiation.

In an advantageous embodiment of the invention, at least one face end ofthe hollow-cylindrical commutator body is closed with a cap made of amaterial that shields against or absorbs electromagnetic radiation. Thecap is provided with a central through opening for the rotor shaft andserves to brace the commutator on the rotor shaft of the electricalmachine. The cap may also be embodied integrally with thehollow-cylindrical commutator body, lending the commutator body theshape of a cup.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail herein below, withreference to the drawings, in which:

FIG. 1 is a perspective view of a commutator for a commutator machineembodying the invention;

FIG. 2, a view of the commutator in the direction of the arrow II inFIG. 1;

FIG. 3, an enlarged perspective view of a connection hook of thecommutator in FIG. 2;

FIG. 4, a perspective view of a cap for covering the face end of thecommutator in FIG. 1;

FIG. 5, a cross section through the commutator in a further exemplaryembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The commutator, shown in perspective in FIG. 1, for an electricalmachine, in particular for an electric motor for actuating drives invehicles, has a hollow-cylindrical commutator body 11 with an outerjacket face 111 and an inner jacket face 112. The commutator body 11 isof an electrical insulation layer, and on its inner jacket face 112 ithas many commutator laminations 12, disposed side by side with gapspacing in the circumferential direction, which extend over the entireaxial length of the commutator body 11. Each commutator lamination 12,on one end, has a terminal lug or a connection hook 14 (FIG. 2). Thecoils of an armature or rotor winding are suspended from the connectionhooks 14, one of which is shown enlarged in FIG. 3, and connectedmechanically and electrically to them in a known manner. The connectionis typically made by so-called hot stacking, which is a hot pressingprocess in which the connection hooks 14 are pressed onto the commutatorlaminations 12, and at the same time the insulation of the armaturewinding wire is melted off in the region of the connection hooks 14.

A cap 15 is placed on the face end, facing away from the connectionhooks 14, of the commutator body 11 and is solidly joined to thecommutator body 11, for instance by being screwed on or by adhesivebonding. The cap 15 is of a material which shields against or absorbselectromagnetic radiations. The cap 15 has a central through opening 16for the rotor shaft 17 (FIG. 5) and serves to brace the commutator onthe rotor shaft 17 axially nondisplaceably and in a manner fixed againstrelative rotation. The cap 15 may also be made integral with thecommutator body 11 by embodying the commutator body 11 in the form of acup, so that the cap 15 is formed by the cup bottom.

As can be seen from the sectional view in FIG. 5, in which the rotorshaft 17 is also shown in section, a brush holder 18 is disposed in theinterior of the commutator body 11 and has two diametrically opposedcommutator brushes 19 on the commutator body 11 that rest on thecommutator laminations 12. The brush holder 18 has a three-dimensionallyfixed support ring 20, on which two brush holders 21 are disposeddiametrically opposite one another. Each brush holder 21 receives onecommutator brush 19 axially displaceably. Each commutator brush 19 ispressed radially onto the commutator laminations 12 by a brush-pressingspring, not shown, and is in electrically conductive contact with anelectrical pigtail 22.

In operation of an electric motor, such as a direct current motor,equipped with such a commutator, sparks occur upon every commutation,since in commutation, the coils of the armature or rotor winding areshort-circuited by the commutator brushes 19 for a very brief period oftime, and their short circuit is then broken again. This sparkdevelopment engenders an electromagnetic interfering radiation, whichhas both a high-frequency interference component that is generated bythe developing electrostatic field and a low-frequency interferencecomponent that is generated by the developing magnetic field. By meansof the shifting, done here, of the commutator laminations 12 and thebrush holder 18 into the interior of the commutator body 11, a greatproportion of this electromagnetic interfering radiation is shieldedagainst by the commutator itself. The cap 15 assures that theelectromagnetic radiation is also unable to escape from the commutatorin the axial direction, or can do so only in damped fashion.

If an even higher degree of interference suppression is required,then—as is shown in FIG. 5—the outer jacket face 111 of the commutatorbody 11 is provided with a layer 23 that because of its materialproperty damps the electromagnetic interfering radiation still moreextensively. Such a layer 23 may for instance be a metal sleeve.

In an alternative exemplary embodiment, for the reinforced damping ofthe electromagnetic interfering radiation, the commutator body 11 ismade from a material that absorbs electromagnetic radiation. Such amaterial is obtained for instance by adding admixtures of magneticallyand/or electrically conductive materials to the plastic. For instance,steel fibers are integrated with the plastic, or carbon in the form ofsoot is admixed with the plastic. In the first case the low-frequencyinterference components of the electromagnetic interfering radiation aredamped more extensively, and in the second case it is thehigher-frequency interference components that are damped moreextensively. It is understood that both material components may beadmixed with the plastic as well. The commutator body 11 may also be ofmetal, in which case an insulation layer should be provided between thecommutator body 11 and the commutator laminations 12.

The cap 15, with its property of absorbing interference radiation, isproduced from the same material as described above.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

1. A commutator for an electric motor for actuating drives in vehicles,the commutator consisting of a hollow cylindrical commutator body (11)having inner and outer jacket faces (112; 111), and commutatorlaminations (12) disposed on the inner jacket face (112) of thecommutator body (11), wherein the commutator body (11) is of plastic,with admixtures of a magnetically and/or electrically conductivematerial that shields against electromagnetic radiation.
 2. Thecommutator of claim 1, further including a layer (23) on the outerjacket face (111) that adds additional shielding against electromagneticradiation.
 3. The commutator of claim 2, and combined with it at leasttwo commutator brushes (19) pressed radially onto the commutatorlaminations (12) in the interior of the commutator body (11), thebrushes (19) being disposed in fixed fashion relative to the commutatorbody (11).
 4. The commutator of claim 1, wherein the admixtures includesteel fibers.
 5. The commutator of claim 4, and combined with it atleast two commutator brushes (19) pressed radially onto the commutatorlaminations (12) in the interior of the commutator body (11), thebrushes (19) being disposed in fixed fashion relative to the commutatorbody (11).
 6. The commutator of claim 1, wherein the admixtures containcarbon.
 7. The commutator of claim 6, wherein the carbon is admixed inthe form of soot.
 8. The commutator of claim 1, and combined with it atleast two commutator brushes (19) pressed radially onto the commutatorlaminations (12) in the interior of the commutator body (11), thebrushes (19) being disposed in fixed fashion relative to the commutatorbody (11).
 9. A commutator for an electric motor for actuating drives invehicles, the commutator consisting of a hollow cylindrical commutatorbody(11) having inner and outer jacket faces (112; 111), and commutatorlaminations (12) disposed on the inner jacket face (112) of thecommutator body (11), wherein the commutator body (11) is of plastic,with admixtures of a magnetically andlor electrically conductivematerial that shields against electromagnetic radiation, and furtherincluding a cap (15) of a material shielding against electromagneticradiation covering at least one face end of the hollow-cylindricalcommutator body (11).
 10. The commutator of claim 9, and combined withit at least two commutator brushes (19) pressed radially onto thecommutator laminations (12) in the interior of the commutator body (11),the brushes (19) being disposed in fixed fashion relative to thecommutator body (11).
 11. The commutator of claim 9, further including alayer (23) on the outer jacket face (111) that adds additional shieldingagainst electromagnetic radiation.
 12. The commutator of claim 9,wherein the admixtures include steel fibers.
 13. The commutator of claim9, wherein the admixtures contain carbon.